The present invention relates to a gypsum castings composition and casting method. More particularly, this invention relates to a gypsum casting composition which is particularly useful as a gypsum dental casting and to a method for producing gypsum dental or similar castings.
For the purpose of the present invention, gypsum and gypsum compositions are defined as materials that are chemically structured as or with calcium sulfates (CaSO4),calcium sulfate dehydrate, calcinated calcium sulfate, or calcium sulfate hemihydrate as a reactive, setting or hardening component. They that are supplied as dry powders and are intended to be mixed with water to a slurry consistency and react with the water to harden into a set mass, mold or casting.
Gypsum for use in the production of castings is traditionally supplied as a dry powder that is extremely hygroscopic.
Dry gypsum powders intended for use in making gypsum dental castings are traditionally supplied as packaged in paper or plastic bags or corrugated boxes or fiber pails etc. in weight volumes of 25, 50, or 100 pounds and sometimes lesser quantities. For example, in one of the more prevalent methods for making gypsum dental castings the gypsum work area is located adjacent to a sink. The gypsum powder is transferred from its bulk package container to a plaster bin where it is stored and may be readily available. The process of transfer requires lifting a heavy weight package and then a messy, dusty task of emptying the dry powder into a storage bin. This transfer of gypsum powder to the storage bin releases dust into the surrounding air and causes cleanup requirements throughout the office. The dust also settles and in time absorbs moisture from the air thereby setting and clogging vents, cabinets, latches, control panels, dials, door hinges, and all nearby mechanical and electrical appliances and components.
The storage bin is traditionally compartmented to accommodate 25 to 50 lbs. of dental plaster, 25 to 50 lbs. of dental stone, and 25 to 50 lbs of dental die stone. These are different types of calcium sulfate hemihydrate determined by the temperature and method of calcining by a manufacturer.
Each type offers a different degree of hardness or set expansion. The transfer process is repeated each time one type of gypsum is emptied and needs replenishment.
To make a gypsum dental casting, the cover to the bin is opened and a measure of gypsum is removed and placed into a container on a weight scale. The amount is adjusted to a pre-determined weight. A measure of liquid is then placed into a measuring beaker. Manufacturers recommend a suggested liquid/powder ratio to achieve a pre-determined specification for set time, controlled expansion and hardness. Excess or insufficient liquid in the mix may affect the physical properties of the set casting. In practice however, the gypsum worker routinely desires to alter the physical properties of set time, hardness or expansion. This is time consuming, requires additional items of preparation such as a scale and a beaker, and increases the amount of gypsum dust that is dispersed into the air and spilled onto and around the work area. Extra cleanup time is additionally required for each of the items in use and the general cleanup of the work area.
The weighed gypsum powder and measured liquid is then transferred to a stiff rubber or vinyl mixing bowl. Mixing bowls are the preferred vessels for the preparation of gypsum and consistently produce predictable results. For general and routine small batch mixes, a stiff bladed spatula is used for the required vigorous stirring of the gypsum until a creamy paste/slurry is achieved. For large batches, a mechanical mixer/bowl device is recommended. The manipulation and transfer of gypsum powder to the mixing bowl further releases dust into the surrounding air. In effect every time the gypsum bin is opened, every time gypsum is transferred to a weight scale and every time gypsum is transferred to a mixing vessel, the powder dust is released into the surrounding air.
When the gypsum powder and the water are mixed to a slurry they are poured into a mold and allowed to set. All of the items used in the preparation of the mix are soiled with gypsum paste and must then be washed. This is the reason that gypsum work areas are traditionally located adjacent to a sink. This then creates an additional problem. The constant washing of gypsum items causes gypsum to build up in the pipes, plumbing and drains of the sink. Most gypsum work area sinks must be equipped with plaster traps that require frequent cleaning or plumbing repairs.
When the gypsum casting is set and returned to its dehydrate the problems of handling are still not ended. When the dry gypsum powder is mixed with water and allowed to set into a casting, the resulting casting is physically a reconfiguration of the original gypsum as mined. Gypsum is well known to have a characteristically, dry, chalky surface. Handling of the finished castings by workers has an irritating effect on the skin of the gypsum workers causing a drying and chaffing. In effect, it is the surface of the gypsum dusting off, through handling. This chalky surface is also traditionally weak and scratches easily producing more dust.
Attempts to reduce the problem of dust by formulating gypsums with various chemical additives have been disclosed such as in U.S. Pat. Nos. 4,911,759, 4,670,053, 5,698,610, 4,909,847 and 4,543,372. There has been little if any improvements utilizing these methods. Dust and mess continue to be a problem. Mixing bowls and utensils still need to be washed and sinks continue to be clogged.
U.S. Pat. Nos. 5,709,467, 5,618,105, 5,465,833 and 5,052,554 disclose a method of mixing gypsum compositions in a disposable plastic bag that is flexible and allows the gypsum mix to be kneaded. The physical constraints of a flexible bag and the kneading method prevent the gypsum from being vigorously stirred or agitated, as is usually required for dental castings. In addition once the bag is filled, water added and kneaded, its jelly-like form is difficult to properly manipulate and to portion out the slurry by squeezing and continual readjustment with one hand while holding and vibrating a mold with the other hand. The larger the bag the more difficult it becomes. The bag mixing techniques additionally makes it difficult for a worker to use a spatula to scoop out a portion of the paste mix and place it onto or into specific areas for shaping or building such as when articulating upper and lower dental casts or filling a void. There is commercially available, gypsum that is packaged in small unit size foil bags. This supply method reduces to some degree the dust associated with transferring the dry powder from a bulk container to a gypsum bin.
This small unit packaging still produces dust to the immediate breathing hazard of the worker when it is emptied into a mixing bowl for preparation of the mix with liquid and has not eliminated the problems of washing utensils and clogging of the sinks, or the dusting off of the surface of the set gypsum.
U.S. Pat. Nos. 4,299,790, 3,958,997 and 3,989,220 disclose a shaker-mixer-molding assembly and a gypsum composition. These methods and compositions do not address or reduce the dusting problem associated with measuring, weighing and transferring a dry gypsum powder from a bulk packaging container or from a bulk storage container to a mixing vessel. Neither do they eliminate the need to wash the mixing vessel, measuring devices and mix utensils in preparation for the next mix. They are related to a performance composition and a speedy method of direct filling a specific mold that is attached by design to the mixing vessel, an object of which is a molding apparatus which is a principle part of the shaker-mixer assembly for matched attachment and pouring.
Similar to the shaker-mixer-mold device of U.S. Pat. Nos. 3,958,997 and 3,989,220 but without the attached mold, there is commercially available a pre-loaded syringe, containing an alginate composition dry powder encapsulated within the lower portion of the syringe. In the upper portion of the syringe and separated by a thin membrane is encapsulated a pre-measured amount of liquid. To make a dental impression mold the pre-loaded dual compartmented syringe is first fitted to a mechanical device that punctures the internal membrane allowing the powder and liquid to combine. The syringe is secondarily placed into a separate electro-mechanical shaker device that vigorously shakes the syringe for a specified time. The syringe is thirdly placed into a separate mechanical plunger device that is used to force the mixed material into an impression tray for the molding process. With this device the pre-measured amounts of both the powder and the liquid are sealed in a single unalterable container device and the volumes are determined and controlled by the manufacturer.
This denies the gypsum worker the required freedom to alter the liquid/powder ratio to obtain molds or castings of variable physical properties or to add a filler, additive or aggregate to the powder as is sometimes desirable or necessary. Additionally, as a practical matter this apparatus with its internal membrane to separate powder and liquid requires specialized filling, loading and assembly machinery by the manufacturer.
Together with all of the required mechanical and electro-mechanical devices necessary for its proper function, it is costly, time consuming and impractical to the large scale production of volume gypsum castings or alginate impression molds.
Similar to the commercially available pre-loaded syringe, U.S. Pat. No. 5,743,431 discloses a fluid dispenser and activator adaptor. This device primarily provides for dispensing of fluid pastes cements, chalking compounds, resins, lubricants and silicone type impression materials. Mixing of two part dry powder and water materials are not discussed.
Attempts to strengthen and harden gypsum appear to have focused on the overall strength and hardness verses the surface durability and/or improving the surface texture.
U.S. Pat. No. 5,026,428 discloses an aqueous solution of boric oxide that is converted to boric acid in water and silicic acid. This solution is mixed with gypsum to increase the overall hardness and decrease the setting time.
U.S. Pat. No. 4,148,660 discloses a gypsum composition that contains perlite and non-fibrous fillers such as silica and mica.
U.S. Pat. No. 4,268,310 discloses a gypsum composition containing formaldehyde a hydrocarbon and magnesium aluminum silicate.
Several U.S. Patents discuss and disclose the use of gypsum/Portland cement combination products with improved hardening or accelerated set properties, or with unique, industry specific, desirable properties. For example U.S. Pat. No. 5,560,774 discloses a method for accelerating the setting time and hardening of hydraulic binders and eliminating the worker and machinery hazards of traditional accelerators by the addition of calcium aluminate, calcium sulfoaluminate and aluminum sulfate. U.S. Pat. No. 4,196,008 uses Carboxy methyl cellulose to maintain strength while rendering the slurry pumpable. U.S. Pat. No. 4,762,561 strengthens basic concrete by reducing the normal levels of iron oxides in the mix.
A consequence of adding chemical adulterants to gypsum is the undesirable effect that such additives have on the dimensional integrity of the set casting. The result is usually a casting with excessive expansion and reduced accuracy. In some instances accuracy is not important as for example with small figurines. In other castings such as for dental, and foundry castings or molds, accuracy and expansion are very critical.
Chemical additives may also adversely effect the set time of gypsums thereby extending work projects. The use therefore of any chemical additive for the improvement of one aspect of a gypsum casting should be carefully selected or formulated to maintain the desirable qualities of no delayed setting time and reliable dimensional accuracy.
U.S. Pat. No. 3,407,924 teaches using a unit-size container for a vacuum treated gypsum that is to be used as a mixing vessel to provide the dental casting composition. This container for some reason is not widely used in the dental industry. This is most likely due to the extra step of vacuum treating the gypsum. This patent does not suggest nor teach the advantageous use of the dental casting compositions of the present convention.
Therefore while the aforementioned traditional methods and patents disclose a variety of devices and methods for producing gypsum castings, and accomplish to a degree their intended objectives, the gypsum dust and handling problems continues to present problems.
Accordingly, it is an object of the present invention to provide a multi-part aqueous gypsum dental casting composition that has a first gypsum composition and a second water composition. The casting composition has either or both a compound and an acid. The compound is selected from ammonium chloride, potassium chloride, ammonium fluorosilicate, magnesium fluorosilicate, magnesium sulfate, magnesium aluminum sulfate, aluminum sulfate, aluminum ammonium sulfate, and non-reactive mixtures thereof. The compound is in either or both of the first and second composition. The acid is selected from oxalic acid, boric acid, phosphoric acid, citric acid, sodium citric acid, tri-sodium citric acid, tartaric acid, sulfuric acid, acetic acid, formic acid, malic acid, ascorbic acid, aspartic acid and mixtures thereof. The acid is in either or both of the first and second composition. When the casting composition is free of the compound, there are at least two of the acids. The first and second compositions are maintained separately and mixed when the casting is to be prepared.
A still further object of the present invention is to provide the dosage size gypsum dental casting shaped container wherein, the shaped container contains 50 to 600 gms of gypsum and contains per 100 parts by weight of gypsum (a) 0.2 to 12 parts by weight of at least one compound selected from ammonium chloride, potassium chloride, ammonium fluorosilicate, magnesium fluorosilicate, magnesium sulfate, magnesium aluminum sulfate, aluminum sulfate, aluminum ammonium sulfite, and non-reactive mixtures thereof, and 0.2 to 18 parts by weight of at least one acid selected from oxalic acid, boric acid, tri-sodium citric acid and phosphoric acid or (b) 0.2 to 24 parts by weight of at least two of the acids.
A still further object of the present invention is to provide a multi-part gypsum casting system which a first gypsum part and a second water part, the total content of the system being for every 100 parts by weight of gypsum, there are 20 to 40 parts by weight of water, and (a) 0.2 to 12 parts by weight of at least one compound selected from ammonium chloride, potassium chloride, ammonium fluorosilicate, magnesium fluorosilicate, magnesium sulfate, magnesium aluminum sulfite, aluminum sulfate, aluminum ammonium sulfate, and non-reactive mixtures thereof; and 0.2 to 18 parts by weight of at least one acid selected from the following acids: oxalic acid, boric acid, phosphoric acid, citric acid, sodium citric acid, tri-sodium citric acid, tartaric acid, sulfuric acid, acetic acid, formic acid, malic acid, ascorbic acid and, aspartic acid, or (b) the compound and/or acid being mixed with either or both of the gypsum or water.
The multi-part dental casting composition has at least two separate parts. The first part is a dry gypsum powder such as Hydrocal (U.S. Gypsum Corp.) and the second part is water. Mixed with the gypsum and/or dissolved in the water is 0.2 to 12 parts by weight of at least one compound selected from ammonium chloride (NH4Cl), potassium chloride (KCl), ammonium fluorosilicate [(NH4)2SiF6], magnesium fluorosilicate (MgSiF6), aluminum ammonium sulfate [AlNH4(SO4)2], magnesium sulfate (MgSO4), aluminum sulfate AL2(SO4)3, and non-reactive mixtures thereof. Also it is preferred that there is also mixed with gypsum and/or water 0.2 to 18 parts by weight of at least one acid selected from the following acids: oxalic acid, boric acid, phosphoric acid, citric acid, sodium citric acid, tri-sodium citric acid, tartaric acid, sulfuric acid, acetic acid, formic acid, malic acid, ascorbic acid, aspartic acid, and mixtures thereof. When the casting composition does not contain one of the compounds, then there are at least two of the acids mixed with either or both of the gypsum and water. When only an acid is used, the preferred range is 0.2 to 24 parts by weight of the two acids but this may be as high as 0.2 to 36 parts by weight of the two acids depending on which acid is selected.
The preferred multi-part dental casting composition uses both the acid and compound and has the compound and acid dissolved in the water. The dry gypsum powder is pre-packaged in dosage sized containers by a manufacturer or distributor. The dosage containers are hereinafter defined as xe2x80x9cshaped containersxe2x80x9d that are ridged or semi-ridged, plastic, rubber-like, paper or coated paper disposable containers that generally hold their shape and simulate in form and function a standard gypsum mixing bowl. The preferred shape of the container is a curved side wall to allow complete mixing and a flat bottom to allow easy storage. The dry gypsum powder occupies approximately only xc2xd to xc2xe of the available volume of the container. The shaped container does not include a plastic freezer bag type container as is shown in U.S. Pat. No. 5,709,467.
The shaped containers may be any one of a variety of sizes but for illustrative purposes, generally resembling the packaging of common individual serving, lunch deserts such as pudding or yogurt with a package cover that is sealed and removable, or a half pint milk carton. This unit packaging of the dry gypsum powder component allows the gypsum to be mixed within the unit package container. The unit package may have a resealable cover and/or lid. The water component with any or all of the above compounds and acids dissolved therein is also preferably pre-loaded into unit dosage packages wherein the unit dose of the liquid is matched to the unit quantity of the dry powder such that the liquid/powder ratio is as recommended by the manufacturer. Generally more liquid than necessary is preloaded so that the liquid to powder ratio may be adjusted according to the preference of the user (dentist). Alternatively the liquid may be provided in a bulk container and a re-fillable and re-useable package such as a syringe is provided so that the user may adjust the liquid/powder ratio more conveniently according to the desired physical properties of the casting.
When a re-sealable container is used, the cover is removed or pierced with a syringe needle to mix the water component with the gypsum. Then the container is re-sealed and the gypsum and water mixture are vigorously mixed by being vigorously shaken by the user or by a mechanical shaker similar to those used to mix paint. Thereafter, the cover is removed and the gypsum slurry may be poured into or packed onto any intended mold or configuration directly from the unit package that has also served as the mixing vessel.
The resulting gypsum dental casting displays no delayed setting time, decreased setting expansion and it has a smooth, silky and glossy, durable surface.
The general configuration of the container is such that it can preferably be used as a mixing bowl that allows easy mixing with a spatula. This being the configuration that a dentist is used to. The container permits the in-situ preparation of the gypsum casting composition and is only partially full with dry gypsum powder so as to be suitable for receiving the liquid component and serving as the spatula mixing vessel.
In one embodiment, for the water component, a larger than unit dose syringe is provided as an easy delivery system for the water component. There are innumerable package configurations that may satisfy the spirit and scope of the invention to including packaging configurations for the liquid component, squeezable or depressible bottles with or without needle like plastic or metal dispensing tips, or combination devices that comprise a single container that includes a container for the dry powder that is suitable for serving as a bowl-like mixing vessel and a volume adjustable liquid container/dispenser or an attached liquid filled pouch.
The above system of multi-containers for the gypsum, compounds and/or acids, and water drastically eliminates the risk of releasing dried gypsum powder into the immediate airspace. Additionally, disposable unit containers provides the convenience of not needing to clean the gypsum powdered bowls, sink area, and not clogging the sink drains. The compounds and acids may be conveniently packaged in separate disposable containers if desired and mixed with the water when they are to be used.